Supercritical vapor generator power plant system



Nov. 3, 1964 w. H. CLAYTON, JR 7 SUPERCRITICAL VAPOR GENERATOR POWER PLANT SYSTEM Filed Dec. 28, 1962 2 Sheets-Sheet 1 INVENTOR W I Li- I AM H. CLAYTON, JR

BY [law A 922% ATTORNEY Nov. 3, 1964 Filed Dec. 28, 1962 w. H. CLAYTON, JR 3,155,079

SUPERCRITICAL VAPOR GENERATOR'POWER PLANT SYSTEM 2 Sheets-Sheet 2 FlC3 2 5 waxes 1,404 .,M

- 6&w MEL INVENTOR WILLIAM H. CLAYTON, JR;

ATTOR NEY United States Patent 3,155,079 SUPERtCRiTlCAL VAYQR GENERATQR NEWER PLANT SYSTEM Wiiliam H. Ciayton, in, Windsor, (Iona, assignor to Combustion Engineering, inc, Windsor, Conn, a corporation of Delaware Filed Dee. 2S, 1962, Ser. No. 247,993 13 Claims. ((11. 122479) This invention relates generally to vapor generatorprime mover systems wherein the vapor generator produces and supplies the motive fluid to a multi-stage prime mover, such as a turbine, with the invention having particular relation to a vapor generator operating at supercri-tical pressure and on the double reheat cycle and having the characteristic that as the load on the unit decreases the percentage of the total heat absorption required by the pressure reheater increases while that required by the low pressure reheater does not increase in order to maintain the two reheat temperatures at a predetermined and desired value throughout a given load range.

In a vapor-power cycle wherein a vapor generator supplies a multi-stage prime mover it is necessary for optimum operating efficiency of the cycle that the vapor that is supplied to the several stages of the prime mover be maintained at a predetermined value throughout the operating load range of the unit. Thus in a vapor generator operating on the double reheat cycle it is necessary to maintain the primary vapor as well as the high pressure and the low pressure reheat vapor at a predetermined temperature throughout the operating load range.

Since the effectiveness of or in other words the heat available to the heat absorbing surface in a vapor generator varies with variation in load it is necessary, in order to obtain the desired temperature control, to provide control actions which will independently regulate the temperature of the primary vapor, the temperature of the high pressure reheat vapor and the temperature of the low pressure reheat vapor. In the supercritical vapor generator of the invention and in accordance with the invention the primary vapor is controlled through the combined regulation of the firing rate and the flow of the primary fluid through the through-flow circuit, while the high pressure and low pressure reheat temperatures are controlled through the combined use of gas tempering and gas recirculation control action and in addition, if desired, adjustment of the zone of combustion in the furnace.

The vapor generator of the invention has an operating, or so-cal-led cycle, characteristic that as the load decreases from maximum the percentage of heat absorption required by the high pressure reheater to maintain the high pressure reheat at its desired value increases while the percentage required by the low pressure reheater either remains generally constant or decreases. The high pressure and low pressure reheaters receive a predominant portion of their heat input by convection and are disposed in the combustion gas stream that is produced by burning fuel in the furnace of the vapor generator in such relation that the low pressure reheater is effectively well upstream of the high pressure reheater with there being primary heat exchange surface forming part of the through-flow circuit of the vapor generator interposed between the e eetive location of the low pressure and high pressure reheater in the gas stream. With this relative disposition of the high pressure and low pressure reheater surface, an independent regulation of each, within limits, can be obtained through the combined action of gas tempering and gas recirculation and as the load on the unit decreases from maximum value the quantity of tempering gas and the quantity of recirculated gas introduced into the furnace is progressively increased with each being regulated in such a manner that the temperature of the two reheats are maintained at their desired value.

In addition to employing gas tempering and gas recirculation con-trol action the zone of combustion may be adjusted with he location of the Zone of combustion being moved away from the furnace outlet with decrease in load. By adjusting the zone of combustion in this manner the quantity of tempering gases that will be required may be reduced over that which would otherwise be necessary.

Accordingly, it is an object of the present invention to provide an improved supercritical vapor generator operating on the double reheat cycle and an improved method of operating the same.

Another object of the invention is to provide such an improved vapor generator and method of operation having the characteristic that as the load decreases the percentage of the total heat absorption required by the high pressure reheat increases while that required by the low pressure reheat remains generally constant or decreases, and wherein the temperature of the primary fluid and the temperature of the high pressure and low pressure reheats are maintained at their desired predetermined values throughout the operating load range of the unit.

Still another object of the invention is to provide such an improved vapor generator and method wherein regulation of the high pressure and low pressure reheat temperatures is effected through the combined action of gas tempering and gas recirculation control.

A still further object of the invention is to provide such an improved vapor generator .and method wherein the control for the high pressure and low pressure reheat temperatures is etfected through the combination of gas recirculation, gas tempering and variation of the zone of combustion control actions.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawings wherein:

FIGURE 1 is a diagrammatic representation, in the nature of a vertical section, of the vapor generator organization of the invention;

FIGURE 2 is a graphic representation showing the effect, at a particular load (for example full load), of gas recirculation and gas tempering control actions on the heat absorption of the high pressure reheater and the low pressure reheater;

FIGURE 3 is a curve indicating the effect of the adjustment of the zone of combustion away from the outlet of the furnace with relation to the heat absorbed by the high pressure and the low pressure reheatens; and

FIGURE 4 is a curve indicating that, of the total heat absorption of the unit, the percentage required by the high pressure reheat increases and the percentage required by the low pressure reheat decreases as the load on the unit decreases and in order to maintain the reheat temperatures at their desired values throughout the operating load range.

Referring now to the drawings, wherein like reference characteristics are used throughout to designate like elements, the illustrative and preferred embodiment of the invention depicted therein includes a forced through-flow vapor generator producing primary vapor at super-critical pressure with the generator supplying a multi-stage turbine and with the vapor generator-turbine combination operating on the double reheat cycle. The supercritical forced through-flow vapor generator includes the upright elongated furnace 10 into which fuel and air are introduced in the lower region thereof with the combustion gases produced through the burning of the fuel passing upwardly through the furnace and out the outlet designated generally 12. xtending from this laterally directed outlet is the gas pass 14 which is connected to the upper end of the downwardly directed gas pass 16 with the gases passing downwardly through this latter gas pass and then through the duct 18 which may lead to an air heater or other conventional equipment and finally being discharged to atmosphere through a stack.

The furnace it) may be fired in any well known manner, such as by means of horizontal cyclones, front wall burner arrangements, tangential firing system or other known arrangements. In the illustrative organization the tangential firing system, such as shown and described in US. Patent 2,697,422, issued December 21, 1954, is depicted with this firing system including the burner organizations designated generally 20 and which include the air or wind box 22 and the burner nozzles 24 with these nozzles being adjustable to adjust the zone of combustion vertical in the furnace between the lower zone identified as A and the upper zone identified as B. Air is supplied to the wind box 22 trough the duct 26 with this air supply being controlled by valve 28 while fuel is supplied to the nozzles 24 through the conduits 3th with this fuel supply being controlled by the valve 32.. These burners are disposed symmetrically about the furnace, which is preferably of rectangular transverse section, and introduce fuel and air into the furnace to create a whirling mass rotating about the axis of the furnace.

The through-flow circuit of the supercritical forced through-flow vapor generator includes the economizer 32, the furnace wall tubes 34, the heat exchange section 36 and the final heat exchange section 38 with these various heat exchange elements or portions being connected in series flow relation. The feed pump 4% forces the primary fluid at supercritical pressure through the throughflow circuit with this fluid first traversing the economizer 32 and thence being conveyed through conduit 42 to the mixing vessel 44. From the mixing vessel the primary fluid is conveyed down through conduit 45 to the lower end of the furnace where this conduit is connected with the headers 48 to which the lower ends of the parallelly disposed tubes that line the inner surface of the furnace wall are connected. The primary fluid. passes up through these furnace wall tubes 34 and into the header t) to which the upper ends of the furnace wall tubes are connected. From the header St) the primary fluid is directed through conduit 52 to the header 54 which is connected with the upper ends of tubes that line the gas pass 15. This fluid thus flows down through these tubes, through headers 55 and 57 and then through the heat exchange section 36. From the heat exchange section the fluid enters the header 56 and then flows through the conduit 58 to and through the final heat exchange section 33 wherein the fluid, which has been vaporized in traversing earlier parts of the through-flow circuit, is heated to its desired temperature and is conveyed through conduit 64) to the high pressure stage 62 of the turbine machine 64.

The exhaust from this high pressure stage n2 is conveyed through the high pressure reheater 65 of the vapor generator where it is reheated to a desired temperature with this exhaust being directed to the reheater 65 through exhaust conduit 66. In passing through the reheater the high pressure reheat or high pressure reheat vapor is heated to its desired predetermined value and is returned to and introduced into the intermediate pressure stage of the turbine through the conduit '72. The exhaust from this intermediate stage of the turbine is conveyed to the low pressure reheater '74- through the conduit 76. In traversing this low pressure reheater the low pressure reheat or low pressure reheat vapor is heated to its desired value and is then introduced through conduit 73 to the low pressure stage St) of the turbine. From this low pressure stage the vapor discharge is conveyed in conventional manner through a condenser, feedwater heater, deaerators, etc. back to the feed pump 40 where the vaporizable fluid is again forced through the throughfiow circuit at supercritical pressure.

In order to obtain optimum efficiency of the power plant, it is necessary that the temperature of the vapor that is delivered in the various stages of the turbine from the vapor generator be maintained at a predetermined value throughout the operating load range of the power plant. In order to obtain this result it is necessary to provide controls which will provide suflicient independent regulation of the primary vapor, the high pressure reheat vapor and the low pressure reheat vapor so that these vapor temperatures can be regulated with varying load. This independent regulation is necessary with regard to the mgh pressure and low pressure reheat vapor for the reason that the heat requirements of the high pressure and low pressure reheats as a characteristic of the operation of the power plant system of the invention on the double reheat cycle, vary with respect to each other as well as with respect to the heat requirement of the primary fluid, with variation in load. As the load is decreased on the vapor generator from the maximum load the percentage of heat absorption with relation to the total heat absorption of the unit required by the high pressure reheater increases relative to that of the low pressure rcheater, with the power plant cycle with which the present invention is concerned being such that the percentage of heat absorption of the high pressure reheater, with relation to the total heat absorption of the unit, increases substantially while this percentage of heat absorption of the low pressure reheat remains generally constant or may decrease whereby a very substantial difference in the heat requirements of the two reheats is had with variation in load. This relation of the heat requirements of the two reheats is graphically illustrated in PEG. 4 wherein the percentage of heat absorption in relation to the total load absorption of the unit is plotted against load.

In accordance with the present invention the final characteristics of the primary fiuid of the forced throughflow supercritical vapor generator are controlled through the combined action of regulating the firing of the vapor generator and regulating the flow of the primary fluid through the primary or through-flow circuit. The former regulation is effected by means of valves 28 and 31 While the latter regulation is achieved by means of valve 81 interposed intermediate the feed pump 40 and economizer 32.

In accordance with the present invention control of the outlet temperatures of the high pressure and low pressure reheat vapors is achieved through the combination of the control action producible by gas tempering and gas recirculation control systems and, if desired, additionally through the adjustment of the zone of combustion in the furnace. The arrangement of the high pressure and low pressure reheat heat exchangers is such that'through the combination of a gas tempering control system and a gas recirculation control system both the high pressure and the low pressure reheat temperatures can be regulated and maintained at their desired value throughout a substantial load range. Both the high pressure and low pressure reheaters are primarily convection, receiving the preponderance of their heat input through convection heat exchange, and they are respectively disposed in the combustion gas stream that is generated by burning fuel in the furnace so that a sufiicient independent control of the heat input thereto is achieved by means of the combination of gas recirculation and gas tempering so that the desired reheat outlet temperatures may be maintained throughout a substantial load range.

In the illustrative embodiment the gas tempering and gas recirculation control systems receive their combustion gases from the lower end of duct 16 by means of the recirculation fan 82. This fan forces these gases through duct 84 and into the gas tempering duct 86 and the gas recirculation duct 88. The gas tempering duct 86 leads to the upper regions of the furnace being connected with distributor 9% which may surround the furnace and have openings leading through the furnace wall into the interior of the furnace. The effect of introducing tempering gases into the furnace is to decrease the temperature of the gases that egress from the furnace, or in other words, temper these gases. Accordingly, the tempering gases are introduced into the furnace and the tempering gas system has its connection with the furnace at a location that is remote from the location of firing and is Well towards the furnace outlet, being relatively close to the outlet. Because of this proximity to the furnace outlet the introduction of tempering gases into the furnace does not decrease the heat absorption in the furnace to any significant extent, although it does decrease the heat absorption of the convection heat exchange surfaces which are closest to the furnace outlet or in other words in the upstream portion of the gas pass extending from the furnace outlet. This effect becomes progressively less further downstream in the gass pass with the heat exchange sections located well downstream having their heat input increased as a result of the introduction of tempering gases into the furnace (see FIG. 2).

The recirculated gas system, or in other words the gas recirculation system, introduces the cooled combustion gases into the lower region of the furnace with gas recirculation duct 88 being connected with the hopper bottom of the furnace. In contrast to the effect produced by tempering gases the so-called recirculation or recirculated gases appreciably decrease the heat absorption in the fluid cooled furnace so that the heat content of the gases egressing from the furnace and passing over the convection heat exchange surfaces is increased. Thus by the introduction of recirculated gases into the lower region of the furnace the heat absorption of the convection heat exchange surfaces in the gas pass is increased with this increase being progressively greater further downstream in the gas pass in relation to combustion gas flow (see FIG. 2).

The amount of tempering gases introduced into the upper region of the furnace end is regulated by damper 92 in duct 86 while the amount of recirculated gases introduced into the lower region of the furnace is regulated by damper 94 in duct 88.

In accordance with the invention the predominantly convection high pressure reheater is so disposed in the gas pass extending from the furnace outlet with relation to the predominantly convection low pressure reheater that it effectively receives a preponderance of its heat input at a location that is well downstream in a combustion gas flow sense from the low pressure reheater with a heat exchanger that forms part of the through-flow circuit of the vapor generator being disposed in the gas pass intermediate of this effective location of the high pressure and low pressure reheaters. The effective disposition of the high pressure and low pressure reheaters is such that the gas recirculation control has a substantially greater effect on the high pressure reheat vapor than on the low pressure reheat vapor, while the gas tempering control has an opposite effect on the high pressure and low pressure reheat vapors. The control effects that are achieved by means of the gas recirculation and gas tempering control systems on the high pressure and low pressure reheat vapors is illustrated in FIG. 2. This figure shows that a a particular load, for example maximum 6 load, an increase in the quantity of recirculation gases from 0 causes a substantial increase in the heat input to the high pressure reheater and gives a considerably smaller increase in heat input to the low pressure reheater. In contrast to this control effect obtained by gas recirculation, an increase in gas tempering from a 0 value results in a substantial decrease in the heat input to the low pressure reheater while giving an increase in the heat input to the high pressure reheater although this increase is less than the decrease of the heat imparted to the low pressure reheater. As a result of this variation in influence of the heat input to the high pressure and low pressure reheaters obtained with gas recirculation and gas tempering an independent regulation of the high pressure and low pressure reheat temperatures can be obtained through the combined action of gas recirculation and gas tempering controls.

As the load on the vapor generator decreases from its maximum value it is necessary to provide control actions, independent of the firing rate, to increase the heat input to both the high pressure and the low pressure reheats. if no such control action was provided the temperature of both of these reheats would steadily drop with decrease in load with the high pressure reheat temperature dropping much more rapidly than the low pressure reheat temperature. With the organization of the present invention, as the load is decreased recirculated gases are introduced into the furnace thereby increasing the heat input to both the high pressure and the low pressure reheat with the increase in heat input to the high pressure reheat being substantially greater than that of the low pressure. However, this gas recirculation control, per se, is incapable of providing the necessary control for both the high pressure and the low pressure reheat temperatures. With the characteristic cycle operation of the vapor generator of the present invention, wherein, of the total heat absorption of the unit, the percentage required by the high pressure reheater rises with decrease in load while that required by the low pressure reheater does not rise but either remains generally at the same value or decreases, the gas recirculation control provides a greater increase in heat input to the low pressure reheater than is necessary to maintain the low pressure reheat temperature at its desired value with decrease in load. This is overcome by simultaneously introducing tempering gases into the furnace with these gases having the effect of decreasing the heat input to the low pressure reheater while increasing, to some extent, the heat input to the high pressure reheater. Accordingly, by suitably regulating the introduction of recirculated gases and the introduction of tempering gases into the furnace both the high pressure and the low pressure reheat vapors may be maintained at their desired value as the load is decreased from maximum and throughout a substantial load range.

The arrangement and operation of the unit may be such that at maximum load there may be little or no recirculated or tempering gases introduced into the furnace, although in order to maintain fan 82 in operation at all times and overcome any problem with regard to backflow through the fan a limited amount of gases may be introduced into the furnace at maximum load. As the load on the unit is decreased from maximum, the amount of recirculated gases introduced into the furnace through duct 88 and the amount of tempering gases introduced into the furnace through duct 86 will progressively increase and with the introduction of these gases being regulated in a manner to maintain the high pressure and the low pressure reheat temperatures at their desired value. This regulation may be automatically achieved and for this purpose there may be provided the temperature responsive device 96 in the outlet line '72 with this device through the controller 98 regulating the damper 94 via the manipulator 100. There is also provided the temperature responsive device 102 in line 78 extending from the outlet of the low pressure reheater and which is effective through the action of controller 1494 and manipulator 1% to adjust the damper 92. Thus the outlet temperature of the high pressure reheater is effectively controlled by regulating the gas recirculating sys tem or in other words the introduction of recirculated gases into the furnace while the outlet temperature of the low pressure reheater is effectively regulated by regulating the gas tempering system, or in other words the quantity of tempering gases introduced into the furnace. Through this combined action both of these temperatures may be maintained at their desired value with varying loads.

The primary vapor issuing from the heat exchange section 38 and conveyed to the high pressure stage 62 of the turbine has its pressure and temperature regulated through the manipulation of the firing rate of the vapor generator and the regulation of the flow into and through the through-flow circuit. For this purpose there is pro vided temperature responsive device 168 and pressure responsor means 110 detecting the temperature and pressure, respectively, of this vapor and through the action of controller 112 being operative to regulate the air flow control valve 28 and the fuel flow control valve 33 via actuators 114 and also being operative to regulate the feedwater control valve 81 via actuator 11s.

The amount of tempering gases necessary to maintain the desired reheat temperatures throughout the predetermined load range may be reduced by combining with the gas tempering system the control achieved by adjustment of the zone of combustion in the furnace. By adjusting the zone of combustion downwardly in the furnace the temperature of the gases egressing from the furnace will be decreased and accordingly the heat input to the low pressure reheater as well as the heat input to the high pressure reheater being decreased. The effect of this adjustment of the zone of combustion is shown in FIG. 3. It is apparent that the effect of this control action is substantially greater on the upstream convection heat exchangers in the gas pass and becomes progressively less further from the gas pass entrance in the direction of combustion gas flow. Thus adjustment of the zone of combustion downward in the furnace It? causes a substantial decrease in the heat absorption of the low pressure reheater with the decrease in heat absorption in the high pressure reheater being much less than that of the low pressure reheater. Accordingly, this adjustment of the zone of combustion may be used to assist in conrolling the high pressure and low pressure reheat temperatures with varying loads and its effect will be to decrease the amount of gas tempering that will be required.

It may be be advantageous to utilize the combination of gas recirculation and gas tempering for a predetermined portion of the load range, i.e., from maximum load down to a predetermined value, and then for the remainder of the load range over which the reheat temperatures are controlled use the combination of gas recirculation and adjustment of the zone of combustion to maintain the reheat temperatures while maintaining the gas tempering at a constant value.

This adjustment of the zone of combustion may be advantageously obtained by tilting the burners 20 with the nozzle 24 being tiltably mounted for this purpose. The arrangement may be such that the nozzle 24 is normally directed in a horizontal direction and when it is desired to achieve the necessary control for the reheat temperatures by adjusting the zone of combustion the nozzles may be tilted down with the combustion zone being adjustable between the zone A and B identified in FIG. 1.

The adjustment of the zone of combustion through manipulation of the burners may be automatic and for this purpose the actuating devices 122 may be regulated by the controller 104 which receives its actuating signal from the temperature responsor device n22 responding to the outlet temperature of the low pressure reheater.

The operation of the burners 20 to adjust the zone of combustion may be automatic and for this purpose the actuating devices 122 may be regulated by the controller 98 which receives its actuating signal from the temperature responsive device 96 responding to the temperature of the vapor leaving the high pressure reheater.

In order to achieve the desired independent regulation of the two reheats, i.e. the high pressure and the low pressure reheat vapor, it is necessary that the effective location of the high pressure and the low pressure reheaters in the combustion gas stream be such that the low pressure reheater is spaced well upstream of the high pressure reheater and that there be interposed between the two reheaters primary heat exchange surface. This is so because if the two reheaters are located immediately one after another the difference in the control effect on each that is obtained by the gas tempering and the recirculation control will, as a practical matter, be insufiicient for achieving the regulation of the two reheat temperatures with varying load. It will be appreciated that while the entire low pressure rehcater has been illustrated as being upstream of the entire high pressure reheater, this arrangement may be varied as required to obtain the necessary heat input to the high pressure and low pressure reheat fluid. For example, a portion of the high pressure reheater may be placed upstream, immediately downstream, or intermediate two portions of the low pressure reheater. However, it is essential that the low pressure reheater receive a preponderance of its heat input at a location in the gas stream which is upstream of the location in the gas stream at which the high pressure reheater receives a preponderance of its heat input and that intermediate these two locations there be provided primary heat exchange surface. With this arrangement an effective control of the two reheat temperatures may be obtained throughout a substantial load range.

In the illustrative forced through-flow supercritical vapor generator there is provided, with relation to the through-flow circuit a recirculating circuit including the conduit 118 into which is connected the pump 119 and valve 120 with this conduit connecting the conduit 52 to the mixing vessel 44. The purpose of this recirculation system is to provide adequate flow through the high heat absorption tubes of the through-flow circuit that line the furnace wall at low loads and during startup, with this arrangement being shown and described in detail in the co-pending application Serial No. 127,395, filed July 27, 1961, with the inventor being Willburt W. Schroedter.

Reference to vapor generator and vapor generation as contained herein is intended to include both steam generators as well as vapor generators using vaporizable fluids other than water. It will be appreciated that in accordance with present-day technology the most practical form of the invention is with a steam generator.

The various heat exchangers that are positioned in the combustion gas stream that is generated in and passes from the furnace are represented schematically in the diagrammatic illustration of FIGURE 1. It will be appreciated that these heat exchangers, in accordance with conventional practice, are comprised of numerous tubular members that are connected in parallel flow with regard to the vaporizable fluid and which are sinuously or otherwise bent to form a tube bundle or group, with it being the general practice to space these tubes in parallel planes across the width of the gas pass or combustion gas stream.

While I have illustrated and described a preferred embodiment of my invention it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein Without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

What is claimed is:

l. A forced through-flow supercritical vapor generator operating on the double reheat cycle and having the characteristic that as the load decreases the percentage of the total heat absorption required by the high pressure reheat increases while that required by the low pressure reheat remains generally constant or decreases, including a furnace into which fuel is introduced and burned and which has an outlet through which the combustion gases thus generated pass, a through-flow circuit through which the primary fluid is passed and including tubular members disposed on the furnace walls, high pressure reheat means and low pressure reheat means positioned in the stream of combustion gases egressing from the furnace with the effective location of the high pressure reheat means being downstream relative to gas flow of the low pressure reheat means and with primary heat exchange surface forming part of the through-flow circuit being positioned in the gas stream intermediate these locations, a tempering gas system and a gas recirculation system associated with said furnace, means operative to controllably increase the quantity of tempering gases introduced into the furnace and the quantity of recirculation gases introduced into the furnace as the load on the unit decreases including means responsive to the low pressure reheat temperature to control the introduction of tempering gases and means responsive to the high pressure reheat temperature to control the introduction of the recirculation gases.

2. A forced through-flow vapor generator operating at supercritical pressure and on the double reheat cycle and having the characteristic that of the total heat absorption of the unit the percentage required by the high pressure reheat increases and that required by the low pressure reheat remains generally constant or decreases with decrease in load and including a fluid cooled furnace, means for introducing and burning a fuel in said furnace with the furnace having a combustion gas outlet remote therefrom, means for regulating the temperature and pressure of the primary fluid including means regulating the flow thereof and means regulating the introduction and burning of fuel in the furnace, high pressure and low pressure reheat positioned in the stream of combustion gases generated by the burning of fuel in the furnace and so distributed that the low pressure reheat means receives a preponderance of its heat input at a first location While the high pressure rheat means receives a preponderance of its heat input at a second location and with said first location being upstream with regard to combustion gas flow of said second location and with heat exchange surface being interposed therebetween and through which the primary fluid is conveyed, means operative to regulate the high pressure and the low pressure reheat temperatures with varying loads including means for introducing cooled combustion gases which have traversed the reheat means into the furnace at a first location remote from the firing means and where little effect is produced upon the heat absorption of the furnace and at a second location remote from the furnace outlet and where a substantial effect upon the heat absorption of the furnace is produced, means responsive to the low pressure reheat temperature operative to regulate the introduction of combustion gases at said first location to increase the same with decrease in load and means responsive to the high pressure reheat temperature operative to regulate the introduction of combustion gases at said second location operative to increase the introduction thereof with decrease in load with this regulation being such as to maintain the two reheat temperatures at their desired value throughout a substantial load range.

3. A forced through-flow supercritical vapor generator operating on the double reheat cycle and having the characteristic that as the load decreases the percentage of the total heat absorption of the unit required by the high pressure reheat increases with relation to that of the low pressure reheat, and including an upright furnace having means for firing the same adjacent its lower region and a combustion gas outlet adjacent its upper region, a throughfiow circuit through which the primary fluid is forced at supercritical pressure and including tubular members on the furnace wall and heat exchange surface in said gas pass, means controlling the temperature and pressure of the primary fluid of the vapor generator including means regulating the firing rate and the passage of fluid through the through-flow circuit, a low pressure reheater effectively positioned in the upstream portion of the gas pass, a high pressure reheater effectively positioned at a location in the gas pass downstream of the low pressure reheater with said heat exchange surface of the through-flow circuit being interposed between these two locations, means operative to withdraw combustion gases from the gas pass at a location downstream of the reheaters and introduce it into the upper portion of the furnace and into the lower portion of the furnace, means responsive to the outlet temperature of the low pressure reheater operative to regulate the introduction of these combustion gases into the upper region of the furnace to increase the same with decreasing load, and means responsive to the outlet temperature of the high pressure heater operative to regulate introduction of these combustion gases into the lower region of the furnace to increase the introduction thereof with decrease in load and with such regulation of the introduction of the combustion gases being effective to maintain the high and low pressure reheat temperatures at their desired value throughout a substantial load range.

4. In a supercritical forced through-flow vapor generator operating on the double reheat cycle and having the characteristic that as the load decreases the percentage of the total heat absorption of the unit required by the high pressure reheat increases while that required by the low pressure reheat remains at least as low as its value at maximum load, said generator including a fluid cooled furnace, a tempering gas system associated with said furnace, a gas recirculation system associated with said furnace, high pressure and low pressure reheat means disopsed in the combustion gas stream produced by the burning of fuel in the furnace with these reheat means being predominantly convection, said low pressure reheat means being disposed in said gas stream at a location such that its heat input is decreased by an increase in gas tempering but is increased by an increase in gas recirculation, said high pressure reheat being located in said gas stream at a location such that its heat input is increased by both an increase in gas tempering and an increase in gas recirculation and the means responsive to said reheat temperatures operative to regulate the gas tempering system and the gas recirculation system to maintain said temperatures at their desired value throughout a substantial load range.

5. In a power plant system, a supercritical vapor generator operated on the double reheat cycle with the percentage of the total heat absorption required by the high pressure reheat increasing and that required by the low pressure reheat decreasing with increase in load and including an elongated furnace having primary heat exchange surface on walls thereof with a combustion gas outlet adjacent one end and being fired at a location remote from said outlet, means to adjust the firing zone toward and away from said outlet, high pressure and low pressure convection reheat means positioned in the combustion gas stream generated in the furnace with the high pressure means being eifectively downstream of the low pressure means, means operative to produce cooled combustion gases into the furnace at a first location relatively close to the furnace outlet and at a second location remote from said furnace outlet, means responsive to the outlet temperature of the low pressure reheat means operative to regulate the introduction of combustion gases at said first location and the adjustment of the zone of combustion in the furnace and means responsive to the outlet teml l perature of the high pressure reheat means operative to regulate the introduction of combustion gases at said second location, whereby said reheat temperatures are regulated throughout a substantial load range.

6. A forced through-flow steam generator operating on the double reheat cycle and having the characteristic that as the load decreases from maximum the percentage of the heat absorption required by the high pressure reheat increases while that required by the low pressure reheat remains generally constant or decreases, said generator including a furnace, means firing said furnace with the furnace having a combustion gas outlet remote from said means, a through-flow circuit through which the primary fluid is conveyed and including heat exchange tubes on the furnace walls and a heat exchanger positioned in the stream of combustion gases generated by the burning of fuel in the furnace, high pressure reheat means and low pressure reheat means positioned in said stream of combustion gases with said low pressure reheat means being effectively upstream of said heat exchanger and said high pressure reheat means being effectively downstream of said heat exchanger, means for adjusting the zone of combustion in the furnace toward and away from said furnace outlet, a gas tempering and a gas recirculation system associated with said furnace, and means operative to increase the tempering gases and move the zone of combustion away from the furnace outlet incident to a decrease in load and means operative to increase the recirculating gases incident to a decrease in load, these last two means including rneanse responsive to the low pressure and high pressure reheat temperatures whereby said temperatures may be maintained at their desired value with variation in load.

7. A supercritical forced through-flow vapor generator operating on the reheat cycle and having the characteristic that as the load decreases from maximum the percentage of total heat absorption required by the high pressure reheat increases while that required by the low pressure reheat decreases said generator including a fluid cooled furnace fired with a suitable fuel and having a combustion gas outlet, means for varying the zone of combustion with relation to said outlet, a gas tempering and a gas recirculation system associated with said furnace, at low pressure reheater disposed so it is influenced predominantly by adjustment of the zone of combustion in the furnace and regulation of the introduction of tempering gases into the furnace, a high pressure reheater disposed so that it is influenced predominantly by adjustment of the recirculating combustion gases into the furnace, means responsive to the outlet temperature of the high pressure and the low pressure reheater and operative to regulatingly increase the introduction of tempering gases and the introduction of recirculating gases into the furnace with decreasing load and regulatingly adjusting the zone of combustion away from the furnace outlet with decreasing load.

8. A supercritical forced through-flow vapor generator operating on the reheat cycle and having the characteristic that as the load decreases from maximum the percentage of total heat absorption required by the high pressure reheat increases with relation to that required by the low pressure reheat, said generator including a fluid cooled furnace fired with a suitable fuel and having a combustion gas outlet, 21 gas tempering and a gas recirculation system associated with said furnace, a low pressure reheater disposed so it is influenced predominantly by regulation of the introduction of tempering gases into the furnace, a high pressure reheater disposed so that it is influenced predominantly by adjustment of the recirculating combustion gases into the furnace, means responsive to the outlet temperature of the high pressure and the low pressure reheater and operative to regulatingly increase the introduction of tempering gases and the introduction of recirculating gases into the furnace with decreasing load.

9. A once through-flow vapor generator operated at supercriticalpressure and on the double reheat cycle having the characteristic that as the load decreases from maximum the percentage of the total heat absorption required by the high pressure reheat increases While that required by the low pressure reheat decreases, a fuel fired, fluid cooled furnace having a combustion gas outlet and means for adjusting the zone of combustion in the furnace, means for introducing cooled combustion gases into the furnace at a first zone close to said outlet and at a second zone remote from said outlet, a high pressure and a low pressure reheater relatively disposed so that the introduction of combustion gases at said second location has its greatest effect on the high pressure reheat while the adjustment of the zone of combustion in the furnace and the introduction of combustion gases at said first location has its greatest effect on the low pressure reheat, control means operative to regulate the temperature of the primary fluid as well as the temperature of the two reheats including means for regulating the ratio of the flow of the primary fluid and the firing rate, and means for increasing the introduction of combustion gases at said first and said second location and adjusting the zone of combustion away from the furnace outlet incident to a decrease in load.

10. In a supercritical forced through-flow vapor generator operating on the double reheat cycle and having the characteristic that as the load decreases the total percentage of heat absorption required by the high pressure reheat increases substantially relative to that required by the low pressure reheat, with the generator having a fiuid cooled furnace into which fuel is fired, a through-flow circuit through which the primary fluid is forced, predominantly convection high pressure and low pressure reheaters with the high pressure reheater being effectively downstream relative to combustion gas flow of the low pressure reheater, the improved method of operation comprising regulating the firing rate and the flow through the through-flow circuit to maintain the final temperature of the primary fluid at its desired value with varying load, introducing cooled combustion gases into the furnace at a first location where they reduced the heat absorption of said low pressure reheater and at a second location where they increased the heat absorption of said high pressure reheater and have a substantially greater effect on the high pressure reheater than on the low pressure reheater,

increasing the combustion gases introduced into the furnace at said first and at said second locations with decrease in load and regulating the two reheat temperatures by regulating this introduction of combustion gases.

11. In a supercritical forced through-flow vapor generator operating on the double reheat cycle and having the characteristic that as the load decreases the total percentage of heat absorption required by the high pressure reheat increases substantially relative to and that required by the low pressure reheat, with the generator having a fluid cooled furnace having a combustion gas outlet and fired with a suitable fuel at a location remote from said outlet, a through-flow circuit through which the primary fluid is forced, predominantly convection high pressure and low pressure reheaters with the high pressure reheater being effectively downstream relative to combustion gas flow of the low pressure reheater, the improved method of operation comprising regulating the firing rate and the flow through the through-flow circuit to maintain the final temperature of the primary fiuid at its desired value with varying load, introducing cooled combustion gases into the furnace at a first location where they reduced the heat absorption of said low pressure reheater and at a second location where they increased the heat absorption of said high pressure reheater and have a substantially greater effect on the high pressure reheater than on the low pressure reheater, increasing the combustion gases introduced into the furnace at said first and at said second locations and adjusting the zone of combustion in the furnace away from the outlet with decrease in load and regulating the two reheat temperatures by regulating these control effects.

12. In a vapor generator operating on the double reheat cycle and including a fluid cooled furnace in which fuel is burned creating a combustion gas stream and having the characteristic that of the total heat absorption of the generator the percent required by the low pressure reheater decreases while that required by the high pressure reheater increases with a decrease in load, the method of operation comprising effectively imparting heat from said combustion gas stream to the high pressure reheat vapor at one location and to the low pressure reheat vapor at another location spaced upstream in a combustion gas flow sense from said onelocation, imparting heat to the primary fiuid from said combustion gas stream intermediate said one and said other location, simultaneously providing a pair of control actions effective to independently control the two reheat temperatures relative to each other with varying load including introducing cool combustion gases into the furnace at a first location where they decrease the heat input to the low pressure reheat vapor while increasing the heat input to the high pressure reheat vapor and at a second location where they increase the heat input to both high pressure and low pressure reheat vapor but have a more pronounced effect on the high pressure reheat vapor, regulating increasing the combustion gases introduced into the furnace at these two locations with decrease in load to maintain the high pressure and the low pressure reheat vapor temperatures at a desired predetermined value.

13. In a supercritical forced through-flow vapor generator operating on the double reheat cycle and including a fluid cooled furnace in which fuel is burned creating a combustion gas stream and having the characteristic that of the total heat absorption of the generator the percent required by the low pressure reheater decreases while that required by the high pressure reheater increases with a decrease in load, the method of operation comprising effectively imparting heat from said combustion gas stream to the high pressure reheat vapor at one location and to the low pressure reheat vapor at another location spaced upstream in a combustion gas flow sense from said one location, imparting heat to the primary fluid from said combustion gas stream intermediate said one and said other location, regulating the final characteristics of the primary fluid by regulating the firing rate and the flow of the primary fluid, simultaneously providing a pair of control actions effective to independently control the two reheat temperatures relative to each other with varying load including introducing cool combustion gases into the furnace at a first location where they decrease the heat input to the low pressure reheat vapor while increasing the heat input to the high pressure reheat vapor and at a second location where they increase the heat input to both high pressure and low pressure reheat vapor but have a more pronounced effect on the high pressure reheat vapor, regulatingly increasing the combustion gases introduced into the furnace at these two locations with decrease in load to maintain the high pressure and the low pressure reheat vapor temperatures at a desired predetermined value.

14. In a forced through-flow vapor generator operating on the double reheat cycle and including an elongated fluid cooled furnace having a combustion gas outlet adjacent one end and fired at a location remote therefrom, said furnace having associated therewith a gas tempering system and a gas recirculation system with the generator having the characteristic that of the total heat absorption of the unit the percentage required by the low pressure reheater decreases while that required by the high pressure reheater increases as the load on the unit decreases from maximum, the improved method of imparting the predominant heat requirement of the low pressure reheat vapor thereto by passing the same in heat exchange relation with the combustion gas stream produced by burning fuel in the furnace and at a location where the introduction of tempering gases into the furnace decreases the heat imparted to this low pressure reheat vapor and imparting the predominant heat requirement of the high pressure reheat vapor thereto by passing the same in heat exchange relation wtih said combustion gas stream at a second location downstream of said first location and where the introduction of tempering gases and recirculated gases into the furnace increased the heat imparted to this high pressure reheat vapor, regulating the reheat vapor temperatures over a predetermined load range by simultaneously regulating the tempering and recirculated gases introduced into the furnace, increasing the same as the load decreases, and regulating said temperatures throughout another load range by simultaneously regulating the introduction of recirculated gas to the furnace and adjusting the zone of combustion in the furnace by increasing said combustion gas introduction and adjusting the zone of combustion away from the furnace outlet with decrease in load.

15. In a forced through-flow supercritical vapor generator operating on the double reheat cycle and having the characteristic that of the total heat absorption of the unit thepercentage required by the high pressure reheat increases substantially relative to that required by the low pressure reheat with decreased load, said unit having a fluid cooled furnace fired with a suitable fuel, the high pressure and low pressure reheaters being predominantly convection and disposed in the combustion gas stream generated in the furnace at effective locations such that the low pressure reheater is upstream of the high pressure reheater, the method of operation comprising increasing the introducing tempering gases into the furnace as the load decreases from maximum and increasing the introducing recirculated gases in to the furnace as the load decreases from maximum and regulating the introduction of the tempering and recirculated gases with varying load to maintain the final temperature of the high pressure and low pressure reheats at a predetermined value.

16. In a forced through-flow vapor generator operating on the double reheat cycle and having the characteristic that as the load decreases that of the total absorption of the unit the percentage required by the high pressure reheater increases while that required by the low pressure reheater decreases with a decrease in load, said vapor generator including an elongated fluid cooled furnace having a combustion gas outlet adjacent one end and fired with a suitable fuel at a location remote from said outlet and with a gas pass extending from said outlet, the high pressure and low pressure reheaters being predominantly convection with the low pressure being effectively disposed in the combustion gas stream at the upstream portion of the gas pass while the high pressure reheater is effectively spaced downstream therefrom with primary heating surface). interposed therebetween, the improved method of operation characterized by maintaining the two reheat temperatures at a predetermined value and throughout a given range in load from maximum by the simultaneous and regulated introduction of tempering gases and recirculated gases into the furnace at respective locations close to and remote from the furnace outlet with this introduction of gases increasing with decreasing load, and throughout a predetermined further load range by the simultaneous adjustment of the zone of combustion in the furnace and the introduction of recirculated gases thereinto at a location remote from the furnace outlet with the zone of combustion being moved away from the furnace outlet and the recirculated gases increasing with decrease in load.

17. In a power plan installation operating on the double reheat cycle and employing a forced through-flow vapor generator having a fluid cooled furnace fired with a suitable fuel and having predominantly convection heated high pressure and low pressure reheaters disposed in the combustion gas stream with the low pressure reheater being effectively upstream of the high pressure reheater the improved method characterized by providing simultaneous control actions independent of the firing rate operative to regulate the two reheat temperatures throughout a predetermined load range including, in the upper portion of said load range, introducing tempering and recirculated gases into the furnace and regulatingly increasing the same as the load decreases and in the remainder of the load range introducing recirculated gases into the furnace and adjusting the zone of combustion in the furnace by increasing the former and moving the latter in a direction to decrease the temperature of the gases traversing the low pressure reheater with decrease in load.

18. In a supercritical forced through-flow vapor generator operating on the double reheat cycle and having the characteristic that as the load decreases the percentage of the total heat absorption required by the high pressure reheater increases while that required by the low pressure reheater decreases and having a fluid cooled furnace the method of operation comprising burning of fuel in said furnace thereby creating a combustion gas stream, heating the high pressure reheat predominantly by com vection and by passing it in heat exchange relation with the combustion gas stream primarily at one location, similarly heating the low pressure reheat by passing the same in heat exchange relation with the combustion gas stream primarily at a second location upstream of said first location, imparting a portion of the heat evolved by the burning fuel to the primary fluid including passing this fluid in heat exchange relation with the combustion gas stream at a location intermediate said first and said second location, regulating the temperature and pressure of the primary fluid by simultaneously regulating the flow of said fluid and the firing rate of the generator, and regulating the two reheater temperatures with varying load by introducing cooled combustion gases into the furnace at a first location which results in a decrease in heat absorption of the low pressure 'reheater and an increase in heat absorption of the high pressure reheater and at a second location which results in an increase in heat absorption of both of the reheaters, regulatingly increasing the cooled combustion gases introduced at these two locations with decrease in load to maintain the two reheat temperatures at their desired value.

References Cited in the file of this patent UNITED STATES PATENTS 2,960,972 Schaap Nov. 22, 1960 2,984,984 Dickey May 23, 1961 FOREIGN PATENTS 550,372 Belgium Sept. 15, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 l55 O79 November 3 1964 William Ho Clayton, Jr.

ified that error appears in the above numbered pat- It is hereby cert hat the said Letters Patent should read as ent requiring correction and t corrected below.

Column 4, line l, for "load" read heat column 5 line 75, for "a a" read at a column 9 line .42 after "reheat" insert means column l3 line 26 'flfor "regulating" read regulatingly column l4 line 71 for "plan" read plant Signed and sealed this xeth day of April 1965. I

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents ERNEST W. SWIDER Altesting Officer 

1. A FORCED THROUGH-FLOW SUPERCRITICAL VAPOR GENERATOR OPERATING ON THE DOUBLE REHEAT CYCLE AND HAVING THE CHARACTERISTIC THAT AS THE LOAD DECREASES THE PERCENTAGE OF THE TOTAL HEAT ABSORPTION REQUIRED BY THE HIGH PRESSURE REHEAT INCREASES WHILE THAT REQUIRED BY THE LOW PRESSURE REHEAT REMAINS GENERALLY CONSTANT OR DECREASES, INCLUDING A FURNACE INTO WHICH FUEL IS INTRODUCED AND BURNED AND WHICH HAS AN OUTLET THROUGH WHICH THE COMBUSTION GASES THUS GENERATED PASS, A THROUGH-FLOW CIRCUIT THROUGH WHICH THE PRIMARY FLUID IS PASSED AND INCLUDING TUBULAR MEMBERS DISPOSED ON THE FURNACE WALLS, HIGH PRESSURE REHEAT MEANS AND LOW PRESSURE REHEAT MEANS POSITIONED IN THE STREAM OF COMBUSTION GASES EGRESSING FROM THE FURNACE WITH THE EFFECTIVE LOCATION OF THE HIGH PRESSURE REHEAT MEANS BEING DOWNSTREAM RELATIVE TO GAS FLOW OF THE LOW PRESSURE REHEAT MEANS AND WITH PRIMARY HEAT EXCHANGE SURFACE FORMING PART OF THE THROUGH-FLOW CIRCUIT BEING POSITIONED 